Proceedings of the British Association. 355 



granitic and the slate systems. In support of this view, he instan- 

 ced more particularly the mines in the vicinity of Marazion, where 

 the lodes or mineral veins traverse lines of elvans obliquely, and 

 where very rich bunches of ore have been obtained at such junc- 

 tions. Indeed the miners of that part of the country are perfectly 

 aware of the value of these junctions, and carry their work on as 

 much as possible within their favorable influence. The author di- 

 rected the attention of the Section to the fact, that all the great 

 mines of Cornwall are situated amid the above conditions, and to 

 the advantages which geology could thus confer upon the communi- 

 ty, by pointing out to them those places where the chances are fa- 

 vorable to mining operations, and by Inducing them to avoid those 

 bubble speculations at this moment so unfortunately common. — Mr. 

 Hopkins was called upon to make some observations regarding the 

 direction of the fissures mentioned by Mr. De la Beche, but he did 

 not enter very full}^ Into any discussion, as he proposed, on the fol- 

 lowing day, to bring the general consideration of fissures before the 

 Section. He observed, however, that there must have been one 

 great axis of disturbance, to which the smaller fissures must either 

 have been parallel, or hav^e circulated around it; indeed, Mr. De la 

 Beche has supposed the great line of fissures from Blackdown to 

 Cornwall had been curved by the Intervening granites. He stated, 

 that there must be a connexion between the width of lodes and their 

 mineral contents ; also, that in the production of fissures there must 

 have been several periods of elevation. — Mr. Fox then mentioned 

 a remarkable experiment which he had made upon the yellow sul- 

 phuret of copper, having changed It by electricity into the grey sul- 

 phuret. In a trough a mass of clay was placed, so as to divide it 

 into two portions, in one of which was sulphate of copper in solu- 

 tion, in the other dilute sulphuric acid. On the electric communi- 

 cation being made by placing the yellow sulphuret in the solution of 

 sulphate of copper, and a piece of zinc In the acid, the change of 

 sulphuret took place, and crystals of native copper were also formed 

 upon it. — Mr. Fox observed, that native copper is not found in the 

 mines of Cornwall combined with yellow copper, but with black 

 copper ore ; and that the grey ore is generally found nearer the 

 surface than the yellow, and also in and near the cross courses. — 

 Mr. Taylor bore testimony to the importance of geological Informa- 

 tion to mining agents, who now were informing themselves, not 

 only in practice but in theory. He spoke of the exertions of the 



